In an 88-page document providing ethical guidelines for such transplants, the Vatican reaffirmed ​an earlier teaching and said the Church has ​no objection to such treatments, provided they follow ⁠best medical practices and do not treat animals with ​cruelty.

“Catholic theology does not have preclusions, on a religious ​or ritual basis, in using any animal as a source of organs, tissues or cells for transplantation to human beings,” the document ​said.

The text addressed xenotransplantation, or the transplanting of ​organs or tissues from one species to another. The Vatican first ‌greenlit ⁠such procedures in 2001, when they were in very early stages of development.

Animal organ transplants for human use are still rare. The first pig-to-human kidney transplant was carried out ​in the ​United States in ⁠2024.

The Vatican document, which was drafted with the help of doctors from Italy, ​the U.S. and the Netherlands, called on scientists ​to ⁠pursue animal transplants in a manner that is “purposeful, proportionate and sustainable”.

It also called on doctors to disclose the risks ⁠of ​animal transplants, including the probability ​of rejection by a patient’s immune system and the possibility of causing ​infection from microorganisms.